This is a continuation application. The parent proposal, which began on 3/1/80, involved the development of assays to monitor fusion of membrane-bound bodies. Some of the assays were to rely upon mixing of the aqueous phases and others upon mixing of the membrane phases. During the current year, assays based on mixing of the aqueous phases have been developed. Two assays were developed, both of which rely upon appearance of fluorescence coincident with fusion. In one case the sequential operation of two enzymes on a fluorogenic substrate is the basis. In the other, the reversal of fluorescence quenching is the basis of the assay. During the coming year these assays will be applied to several varieties of membranes to determine the conditions under which fusion may be obtained. In general systems will be kept as simple as possible. One group of measurements will involve liposomes constituted of lipids of various types and treated with calcium ion or other agents known or suspected to cause fusion. Another set of experiments will deal with the interaction of Sendai virus with reconstituted liposomes. The purpose of these experiments is to determine whether this virus, which infects cells by fusing with the cell membrane, will also fuse with a membrane, the only protein of which is the receptor for the virus. In case fusion is indicated, we will undertake to determine whether the fusion process involved any covalent modification of the components of the target membrane. In another related project, the effects of enzyme inhibitors on virus-induced hemolysis will be examined. Hemolysis is a consequence of membrane fusion and its inhibition should be an indication that the operation of an enzyme is involved.